Why is it especially kids under 12?! I have seen some very knowledgable kids 12 and under, and some very unknowledgable grown ups, age has nothing to do with it!
He clearly said: especially kids under 12 without any fish keeping education
And as for 12-15 year olds; it's fair to say that in general (again, there are exceptions) they aren't as smart as the average adult. Get used to it, it's just a fact.